CAL-944 Can't invite participant that has emails with a dot "."

Fix description: use emailRegex instead of emailFormat regex in method isAValidEmailAddress.
CAL-850 Can add permission for membership while Notification notices that user does not exist

Fix description: refactor method #getPermissions()
- Check ANY permission (.) first
- Then, check membership type permission (*.MEMBERSHIPTYPE)
- The last, check that user is exising in group by use MembershipHandler#findMembershipsByUserAndGroup(username, groupId) instead of load all user in group then loop